How robots are becoming critical players in nuclear disaster cleanup

Watch Honda’s Asimo humanoid robot up close, and you may fall under its spell. As it walks gracefully across a stage, sometimes opening bottles or serving tea, the elegant mechatronic man seems at home anywhere. So after a 9.0-magnitude earthquake and tsunami waves struck Japan’s Fukushima Daiichi plant on 11 March 2011, it was no wonder that one of Asimo’s fans tweeted, “Can’t Asimo be dispatched to survey the interior of Unit 4, where radiation is too high for human workers?”

If only. In the early days of the crisis, engineers were desperate to learn about the damaged reactors’ cores and the radiation levels inside the buildings, data that robots should have been able to provide. Alas, neither Asimo—designed to navigate sedate offices—nor any other of Japan’s vaunted robots was up to the challenge of navigating Fukushima’s complex, debris-strewn interiors. The plant’s operator, Tokyo Electric Power Company (TEPCO), had to turn to U.S. military-grade robots, such as iRobot’s 510 PackBot, to get its first glimpses inside the facility. Only in June 2011, 2 months later, did a modified Japanese rescue robot called Quince enter one of the ruined complex buildings.

“When Fukushima occurred, I was astounded that Japan had no robots to help out in any significant way,” says Frederik Schodt near San Francisco, California, author of Inside the Robot Kingdom: Japan, Mechatronics, and the Coming Robotopia. “It practically brought me to tears.”

Five years after the accident, however, robots are finally ready to enter the ruined reactors en masse. They are now expected to play an essential part in the daunting task of decontaminating and dismantling the reactors. Roboticists are making halting progress in developing machines for specific tasks, such as decontaminating and removing melted nuclear fuel masses, but they know that their creations need to be adaptable. “We must prepare for unforeseen situations beyond the scope of expectation and imagination,” says Satoshi Tadokoro, a roboticist at Tohoku University in Sendai, Japan, who led development of Quince.

The struggles of Japanese roboticists came despite a national program in the 1980s to develop robotics for nuclear power plants. One of the first was AMOOTY, which Toshiba and University of Tokyo researchers built in 1985. The radiation-hardened crawler could climb stairs and manipulate objects in mock power plants. But in 1999, when an accident at a uranium reprocessing facility in Tokaimura killed two workers and contaminated the plant, AMOOTY was still considered too experimental to use.

We must prepare for unforeseen situations beyond the scope of expectation and imagination.

Satoshi Tadokoro

In the years after Tokaimura, Japan developed other nuclear disaster robots and imported Menhir, a large mobile unit built by France’s Cybernetix that’s equipped with radiation shielding, cameras, and a manipulator. But well before the Fukushima disaster, TEPCO and other industry testers judged them to be too big, slow, and ineffective. Government funding ran out, and Menhir is now on display at Tohoku University. The other machines were mothballed or cannibalized for parts, according to The Asia-Pacific Journal: Japan Focus; misplaced faith in the safety of nuclear plants and lack of long-term funding scuppered the program.

After the catastrophe of 11 March 2011, the first task for robots was to survey damage, radiation, and variables such as temperature and humidity in areas that were too hazardous for workers. The PackBot droids explored the ground floors of the Unit 1 and Unit 3 reactor buildings, and found maximum radiation levels of tens of millisieverts (mSv) per hour. Workers exposed to such levels for less than a workday would exceed their emergency safety limit for an entire year, 250 mSv. The radiation and temperature maps made by the PackBots and two iRobot 710 Kobra bots allowed TEPCO workers to plot paths for quick forays into the reactor buildings with the least radiation exposures, says iRobot Vice President Tim Trainer in Bedford, Massachusetts.

K. Sutliff/Science

But the complex structure of the reactor buildings’ ground and upper floors, with many staircases and thick concrete walls, challenged robot mobility and wireless communications. The iRobot bots couldn’t climb slippery stairs or turn corners easily. Once it was clear that more capable machines were needed, TEPCO and the government contacted roboticists at Chiba Institute of Technology and Tohoku University. They hastily modified Quince, a survey droid on caterpillar treads that climbs stairs and debris, by equipping it with two cameras, a dosimeter, and a power and communications cable that stretched hundreds of meters. Quince explored the upper floors of the Unit 2 reactor building. More sophisticated versions, dubbed Rosemary and Sakura, were also sent into the reactor buildings. Sakura acts as a communications relay, and Rosemary is equipped with a U.K.-developed system that combines radiation meters, a fisheye camera, and a laser rangefinder to produce 3D radiation maps.

By now, nearly a dozen robots have been developed to get closer looks at the heart of the plant. Some float or swim through pools that have formed in the building’s bowels because of the constant need to inject water to cool the damaged cores. Two snakelike robots crawled through a pipe leading into the 48-meter-tall primary containment vessel in the Unit 1 reactor to ascertain the state of melted fuel masses. Although one got stuck, the machines returned valuable video and dose information, according to TEPCO. In the dark and vaporous interior, the robots measured radiation in one area as high as 25 sieverts per hour—enough to kill a person in minutes.

Makers are now developing robots that can tackle specific decommissioning chores. For example, Toshiba has developed machines that decontaminate surfaces with blasts of dry ice, inspect vent pipes for leaks, and cut and remove debris covering fuel rod assemblies in the Unit 3 building, which was damaged by a hydrogen explosion. Honda developed a robot based on Asimo’s joint-stabilization technology that can extend 7 meters vertically to inspect upper nooks. “Every robot needed differs according to its purpose and the damage,” says Tomohisa Ito, a spokesperson for the International Research Institute for Nuclear Decommissioning in Tokyo, a consortium of nuclear plant companies that aims to develop new technologies for cleaning up the Fukushima plant.

Robots’ slow start at Fukushima holds a broader lesson, says Gill Pratt in Boston, an engineer who led the Defense Advanced Research Projects Agency Robotics Challenge from 2012 to 2015 before joining Toyota to head its new artificial intelligence lab. Roboticists, he says, need to develop emergency robotic equipment that can be deployed immediately without the need for additional training or adaptation. “The great lesson of Fukushima,” Pratt says, “is that disasters are often fast moving and difficult to predict events, where the window of time for effective intervention is small.” In the immediate aftermath of a future nuclear accident, robots, and their masters, will have to be far nimbler. But at least at Fukushima, they are evolving.